Method and apparatus for compensating reproduced audio signals of an optical disc

ABSTRACT

An apparatus and method for compensating audio signals to be recorded on an optical disc to optimize usage of memory in an audio decoding circuit, and to neutralize invalid audio data to produce good audio quality. A determination is made with regard to whether audio data signals contain normal data or invalid data. Invalid data is adjusted into normal audio data, and stored in the memory. The volume of the data stored in the memory is monitored to detect overflow and underflow conditions of the memory, a data transmitting stopping signal being sent during an overflow condition of the memory, a data transmitting requesting signal being sent during an underflow condition. The audio data reproduced from the memory is decoded, and the decoded audio data is output. Undesired errors are prevented by monitoring the reproduced audio data for invalid data and by adjusting invalid data into normal data when detected.

This application is a divisional of application Ser. No. 09/866,728,filed on May 30, 2001, now U.S. Pat. No. 6,408,040 which is acontinuation of application Ser. No. 08/985,631, filed on Dec. 4, 1997,now abandoned the entire contents of which are hereby incorporated byreference and for which priority is claimed under 35 U.S.C. §120; andthis application claims priority of application No. 97-3399 filed inKorea on Feb. 4, 1997 under 35 U.S.C. §119. This application is aContinuation Reissue Application of U.S. application Ser. No. 11/930,729filed Oct. 31, 2007 now U.S. Pat. No. Re. 42,791, which is a reissue ofU.S. Pat. No. 6,542,564 B2 issued Apr. 1, 2003 (U.S. application Ser.No. 10/055,948 filed Jan. 28, 2002), which is a divisional ofapplication Ser. No. 09/866,728 filed on May 30, 2001 (now U.S. Pat. No.6,408,040), which is a continuation of application Ser. No. 08/985,631filed on Dec. 4, 1997 (now abandoned), which claims priority benefits ofKorean Application No. 97-3399 filed in Republic of Korea on Feb. 4,1997 under 35 U.S.C. §119. The entire contents of the above-identifiedU.S. applications are incorporated by reference. Notice: More than onereissue application has been filed for the reissue of U.S. Pat. No.6,542,564 B2. The reissue applications are application Ser. Nos.11/930,729 filed Oct. 31, 2007; 11/932,846 filed Oct. 31, 2007;11/932,893 filed Oct. 31, 2007; 12/850,590 filed Aug. 4, 2010;12/850,593 filed Aug. 4, 2010; 12/850,594 filed Aug. 4, 2010; 12/850,600filed Aug. 4, 2010; 12/850,602 filed Aug. 4, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for reproducingdata from an optical disc and, more particularly, to a method andapparatus for compensating audio signals reproduced from the opticaldisc.

2. Description of the Prior Art

A Compact Disc (referred to as “CD” hereinafter) is a conventionalrecording medium which records data digitally. Because data is recordeddigitally, it does not deteriorate when reproduced, even if the CD isused repeatedly. However, the CD, which is presently used throughoutaudio and computer fields, has limited recording capacity that restrictsits use in video. A Digital Versatile Disc (“DVD”) has been recentlydeveloped as a new recording medium suitable for the multi-media age inthe recording media market. The DVD is able to store moving images aswell as numbers, characters, figures and voices. The DVD has all theadvantages of the CD, and has a recording capacity of about 5.2 Gbytesper side. Therefore, a complete conventional movie, including movingimages, can be sufficiently recorded on one DVD.

Physically, the DVD is as small and durable as a conventional CD.Furthermore, data stored on the DVD is recorded digitally, rendering itable to be preserved easily. For these reasons, the DVD is analternative recording medium that has become widely used in the marketof recording media including video/audio and computer fields. The wideuse of the DVD in image fields has given the DVD a good reputation as animage recording media.

Conventional reproduction apparatuses for reproducing video/audiosignals from the DVD, and the operation thereof, are described in detailbelow with reference to FIGS. 1 to 4C of the attached drawings.

FIG. 1 is a block diagram showing a conventional reproduction apparatusfor the optical disc. As shown in FIG. 1, the conventional reproductionapparatus comprises: an optical disc (i.e. DVD) 1 on which video/audiosignal data are recorded; an optical pick-up apparatus 3 for reading thedata recorded on the optical disc 1; and a motor 11 for rotating theoptical disc 1; and a servo-circuit 13 for controlling the motor 11 andthe optical pick-up apparatus 3.

The conventional reproduction apparatus further comprises: amicro-processor 15 for managing the overall control of the reproductionapparatus according to a user's request, and for controlling theservo-circuit 13; a navigator 17 for receiving commands from themicro-processor 15, and for executing the commands as to thetransmission of data; and a high frequency amplifying circuit 5 foramplifying data read from the optical pick-up apparatus 3 in highfrequency bands, and for outputting amplified signals under the controlof the navigator 17.

The conventional reproduction apparatus also comprises: an errorcorrecting circuit (ECC) 7 for correcting errors in bit stream ofamplified signals output from the high frequency amplifying circuit 5and for outputting corrected signals under the control of the navigator17; and a Variable Bit Rate buffer (VBR buffer) 9 for temporarilystoring signals output from the error correcting circuit 7 under thecontrol of the navigator 17. The VBR buffer 9 may be a First In FirstOut (FIFO) buffer.

In addition, the conventional reproduction apparatus comprises a datadecoding unit 20 which is composed of a video decoding circuit 21, agraphics circuit 25 and an audio decoding circuit 27. When the bitstream output from the VBR buffer 9 is input to the navigator 17 and thedata decoding circuit unit 20, the video decoding circuit 21 extractsonly video signal data therefrom and decodes the video signal data basedon data dividing control signals of the navigator 17. Similarly, thegraphics circuit 25 extracts and decodes only caption signal data, andthe audio decoding circuit 27 extracts and decodes only audio signaldata.

The video data decoded by the video decoding circuit 21 and the captionsignal data decoded by the graphics circuit 25 are mixed in a mixer (notshown in the attached drawings), and then the mixed data is convertedinto analog signals by a video digital/analog converter 23, which isdisplayed after being adjusted into broadcasting signals in a NTSC/PALencoder 31. In the similar manner, the audio data decoded by the audiodecoding circuit 27 is converted into analog signals by a audiodigital/analog converter 29, which audio data is then synchronized withthe video signals and output.

The operation of the conventional reproduction apparatus of the opticaldisc will be described in the following.

The video/audio data recorded in the DVD is composed of user data andsystem data. The user data is composed of video data formatted in VBRformat which will be processed in the video decoding circuit 21, andaudio data which will be processed in the audio decoding circuit 27. Thesystem data is composed of information relating to systematic functions,by which, for example, the video/audio data selected by the user areread from the DVD and transmitted to the audio decoding circuit 27 andvideo decoding circuit 21 at a suitable rate.

FIG. 2 shows a conventional DVD format. As shown in FIG. 2, the userdata recorded in the DVD 1 is composed of the video data and the audiodata. By comparison, the recording capacities of the video data and theaudio data are arranged such that about 9 frames of the video data arerecorded for every one frame (1536 bytes) of audio data. The disparitybetween audio and video data stored on the disc is a consequence of thedisproportionate size of audio and video frames. The video dataincludes, for example, data corresponding to moving images whichgenerally occupies much more space to than the audio data.

When reproduced from the DVD, the video data and the audio data areadequately amplified. The amplified signals being corrected in the errorcorrecting circuit 7 before being temporarily stored in the VBR buffer9.

The signals output from the VBR buffer 9 are input into the datadecoding unit 20 under the control of the navigator 17, and the datadividing operation is executed in at least one of the decoding circuitsof data decoding unit 20. Then, the divided signals are decoded,respectively, by the following process.

FIG. 3A is a detailed circuit diagram of the video decoding circuit 21illustrated in FIG. 1.

The video decoding circuit 21 comprises a parser 33, a video decodingunit 35 and a memory 37. The parser 33 receives the bit stream from theVBR buffer 9 via a first input terminal and the data dividing controlsignals from the navigator 17 via a second input terminal. The parser 33extracts only the video data in accordance with the data dividingcontrol signals, and outputs the video data to the video decoding unit35. Other video-related signals will be parsed to subsequent stages(such as, the graphics circuit 25 and audio decoding circuit 27). Thevideo decoding unit 35 generates original signals by decoding the videodata extracted in the parser 33. The video decoding unit 35 may alsotemporarily store the decoded data of the original signal in the memory37, and output the original signals stored in the memory 37. The videodecoding unit comprises a control unit (not shown in the attacheddrawings) for monitoring the storage volume of the data stored in thememory 37, and for outputting a data transmitting request signal to thenavigator 17 based on the storage volume of the data stored in memory37.

In other words, the video decoding circuit 21 decodes the video datainput from the parser 33, temporarily stores the decoded video data inthe memory 37, and outputs signals based on stored data when the datacorresponding to a predetermined screen portion are stored. The videodecoding circuit 21 also monitors the storage volume of the data storedin the memory 37, in which the data decoded in the video decoding unit35 are stored. So long as there is memory space in the memory 37, thevideo decoding unit 35 will decode additional video data by outputtingthe data transmitting request signal to the navigator 17. However, ifthe memory 37 is full, the video decoding unit 35 adjusts the input ofvideo data to memory 37 by outputting a data transmitting stoppingsignal to the navigator 17.

FIG. 3B is the detailed circuit diagram of the audio decoding circuit 27included in the conventional device illustrated in FIG. 1. The audiodecoding circuit 27 comprises a parser 39, an audio decoding unit 41 anda memory 43. The parser 39 receives the bit stream from the videodecoding circuit 21 via a first input terminal, and receives the datadividing control signal from the navigator 17 via a second inputterminal. The parser extracts only the audio data in accordance with thedata dividing control signals. Thereafter, the audio decoding unit 41decodes the audio data extracted by the parser 39, and temporarilystores the audio data decoded in the memory 43. In other words, theaudio decoding circuit 27 decodes the audio data input via the parser39, temporarily stores the decoded data in the memory 43, andcontinuously outputs the data stored in the memory 43.

Unlike the video decoding circuit 21, the audio decoding circuit 27 doesnot have any means to output a data transmitting request signal or datatransmitting stopping signal to the navigator 17. That is, in theconventional reproduction apparatus for the optical disc, the rate atwhich the data is input into the audio decoding circuit 27 is adjustedonly according to the storage volume of the data stored in the memory 37of the video decoding circuit 21 used to decode the video data.

As mentioned earlier, the size of recorded video data is about 9 timesthat of recorded audio data, as shown in FIG. 2. The memories 37 and 43are therefore pre-set so that the ratio of the space of the memory 37 inthe video decoding circuit 21 and that of the memory 43 in the audiodecoding circuit 27 is also about 9:1. However, audio data isirregularly recorded at various positions on the DVD, and the decodingoperation of the video decoding circuit 21 is not always synchronizedwith the decoding operation of the audio decoding circuit 27. Therefore,if the audio signal data is input into the audio decoding circuit 27depending on the video decoding circuit 21, audio signals outputted canbecome discontinuous.

In order to overcome the above problem, the memories 37 and 43 may bedesigned so that the ratio of recording space in the memory 37 of thevideo decoding circuit 21 to the recording space in the memory 43 of theaudio decoding circuit 27 is less than 9:1. To achieve this reducedproportion without sacrificing video data memory capacity, the memory 43of the audio decoding circuit 27 must be made larger. However, in suchcase, the cost of the apparatus rises and the memory 43 can not be usedefficiently.

In addition, since the audio decoding circuit 27 can not generate thedata transmitting request and stopping signals independently, theconventional apparatus has another problem in that overflow and/orunderflow of the data occurs in the memory 43 of the audio decodingcircuit 27.

As shown in FIG. 4A, the length of one frame of the normal audio databeing input into the audio decoding circuit 27 is 1536 bytes. The audiodecoding circuit 27 in the conventional reproduction apparatus, as shownin FIG. 2, therefore processes the audio data one frame (1536 bytes) ata time. More specifically, before recording the data in the DVD, audiosignals are processed (e.g. encoding the audio data or inserting theerror correction code in the audio data, etc.) in increments of 1536bytes. Therefore, the audio decoding circuit 27 also has to perform thedata processing operation per 1536 bytes.

However, as shown in FIGS. 4B and 4C, the length of the audio data readfrom the optical pick-up apparatus 3 may be larger or smaller than thenormal length (1536 bytes) due to a disc error or a recording error. Inthese situations, a further problem will occur since the audio decodingcircuit 27 does not decode the audio signal data normally, causing errorsignals to be generated as described hereinafter.

If the size of the bit stream of the audio data being input into theaudio decoding circuit 27 is smaller than 1536 bytes (refer to FIG. 4B),some data of the audio data bit stream of a subsequent frame will beprocessed together with the data of the present frame, causing errors tobe generated. Also, if the bit stream input is larger than 1536 bytes(refer to FIG. 4C), the remaining data after the 1536th byte in thepresent frame will be processed with the data of the subsequent frame.In both cases, the decoding operation of the audio data can not beperformed normally.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the above-mentionedproblems with the conventional reproduction apparatus of the DVD.

It is also an object of the present invention to provide an apparatusand method for compensating reproduced audio signals of the optical discby which the memory in the audio decoding circuit can be used mostefficiently.

It is another object of the present invention to provide an apparatusand method for compensating reproduced audio signals of the optical discwhich result from invalid audio data input due, e.g., to disc errors, toreproduce a good quality sound.

One aspect of the present invention is a method and apparatus forcompensating invalid audio signals by determining whether an audio dataunit has a size that is equal to a predetermined size that is related toa size of a valid audio frame, changing the size of the audio data unitto the predetermined size when it is not equal to the predeterminedsize, and storing the audio data unit into an audio memory. To determinewhether an audio data unit has a size that is equal to a predeterminedsize, header data within the audio data unit is detected, and a size ofthe audio data unit following the detected header is compared to thepredetermined size.

When the audio data unit is smaller than the predetermined size, thesize of the audio data unit may be changed by adding dummy data to theaudio data unit. The dummy data may be muted signal data, or data thatis representative of audio data included in audio data units previouslystored in the audio memory. By contrast, when the audio data unit islarger than the predetermined size, a portion of the audio data unitexceeding the predetermined size may be eliminated, or it may be storedand overwritten with valid audio data unit.

Another aspect of the present invention is a method and apparatus forcompensating invalid audio signals by counting a number of bitsfollowing a header of an audio data unit, detecting a size of the audiodata unit based on the number of bits counted in the counting step, andcontrolling storage of the audio data unit into an audio memory based onthe detected size. When the detected size is smaller than apredetermined size, the storage of the audio data unit is controlled bygenerating dummy data, and adding the dummy data to the audio data unitor replacing the audio data unit with the dummy data. As such, storageof the audio data unit into the memory is prevented when the detectedsize is smaller than a predetermined size. By contrast, when thedetected size is larger than a predetermined size, at least a portion ofaudio data corresponding to the audio data unit exceeding thepredetermined size is prevented from being stored in the audio memory.In this manner, consecutively received audio data units are storedseparately.

Yet another aspect of the present invention is a method and apparatusfor controlling storage of audio data to an audio memory based on amountof data stored in that audio memory. Specifically, the method andapparatus detect an amount of data stored in the audio memory, andcontrolling storage of audio data into the audio memory based on theamount of data stored. The detecting step includes determining whetherthe amount of data stored in the audio memory is less than apredetermined lower threshold, or greater than a predetermined upperthreshold. This can be accomplished by detecting an address of a lastaudio data unit stored in the memory and comparing that detected addressto the predetermined upper and lower thresholds.

If the detected address is less than the predetermined lower threshold,additional audio data may be requested for storage into the audiomemory. If additional audio data is not available, data that isrepresentative of previously stored audio data. By contrast, if thedetected address is greater than the predetermined upper threshold, adata transmission stopping signal is generated and storage of additionalaudio data may be stored in the memory is halted.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of example only, since various changes and modificationswithin the spirit and scope of the invention will become apparent tothose skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionwith the accompanying drawings, which are given by way of illustrationonly and thus are not limitative of the present invention, and in which:

FIG. 1 is a block diagram of a conventional reproduction apparatus of anoptical disc;

FIG. 2 is a diagram of memory space configured for a conventional DVDsystem;

FIG. 3A is a block diagram showing the video decoding circuit 21illustrated in FIG. 1;

FIG. 3B is a block diagram showing the audio decoding circuit 27illustrated in FIG. 1;

FIG. 4A shows the formation of normal audio data having a sizecorresponding to one normal frame;

FIG. 4B shows the formation of invalid audio data having a size smallerthan one normal frame;

FIG. 4C slows the formation of invalid audio data having a size largerthan one normal frame;

FIG. 5 is a block diagram of the reproduction apparatus of the opticaldisc according to the present invention;

FIG. 6 is an internal block diagram showing an audio decoding circuit127 illustrated in FIG. 5;

FIG. 7 is a detailed block diagram showing an audio decoding unit 141illustrated in FIG. 6;

FIG. 8 is an internal block diagram showing a data storage volumedetecting unit 153 illustrated in FIG. 7;

FIG. 9 is a detailed block diagram showing an control unit 155illustrated in FIG. 7, according to a first preferred embodiment of thepresent invention;

FIG. 10 is a state diagram showing a memory 143 illustrated in FIG. 6;

FIG. 11 is a flow chart for the method of compensating reproduced audiosignals in the audio decoding circuit 127, according to the presentinvention;

FIG. 12 is a flow chart showing an invalid data processing routineillustrated in FIG. 11;

FIG. 13 is a flow chart showing an overflow processing routineillustrated in FIG. 11;

FIG. 14 is a flow chart showing an underflow processing routineillustrated in FIG. 11;

FIG. 15 shows a selective preferred embodiment of an audio decoding unit141 according to the present invention when the overflow or underflow isgenerated in the memory 143;

FIG. 16 shows a selective preferred embodiment of the control unit 155according to the present invention illustrated in FIG. 7; and

FIGS. 17A-17F are diagrams showing output waveforms of invalid andcompensated audio signals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5 is a block diagram of the reproduction apparatus for an opticaldisc according to the present invention. As shown in FIG. 5, the opticaldisc reproduction apparatus of the present invention comprises: a DVD101 on which video/audio signals are recorded; a motor 111 for rotatingthe DVD 101; an optical pick-up apparatus 103 for reading the signalsrecorded on the DVD 101; a servo-circuit 113 for driving the motor 111and the optical pick-up apparatus 103; and a high frequency amplifyingcircuit 105 for amplifying the signals read from the optical pick-upapparatus 103.

The reproduction apparatus of the present invention also comprises: amicro-processor 115 or other processing device for managing the overalloperation of the apparatus upon user's demand, and for controlling theoperation of the servo-circuit 113 and the high frequency amplifyingcircuit 105; and a navigator 117 for receiving control signals from themicro-processor 115 and for controlling data transmission.

Further, the reproduction apparatus of the present invention comprises:an error correcting circuit 107 for correcting errors of bit streamsignals output from the high frequency amplifying circuit 105 and foroutputting corrected signals under the control of the navigator 117; anda VBR buffer 109 for temporarily storing the signals output from theerror correcting circuit 107 under the control of the navigator 117. TheVBR buffer 109 may be a First In First Out (FIFO) buffer.

In addition, the reproduction apparatus of the present inventioncomprises a data decoding unit 120 which includes a video decodingcircuit 121, a graphics circuit 125 and an audio decoding circuit 127.The bit stream signals output from the VBR buffer are input into thenavigator 117 and the data decoding circuit unit 120. The video decodingcircuit 121 extracts only video signals from the bit stream signalsinput, and decodes them upon receiving data dividing control signalsfrom the navigator 117. Similarly, the graphics circuit 125 extracts anddecodes only caption signals, and the audio decoding circuit 127extracts and decodes only audio signals.

The audio signal data is decoded into audio data by audio decodingcircuit 127 using the above described process, and the audio data isconverted into audio analog signals which are output synchronously withthe video signal by an audio digital/analog signal converter 129. Videodata decoded in the video decoding circuit 121 and caption data decodedin the graphics circuit 125 are mixed in a mixer (not shown in theattached drawings). The mixed signal output by the mixer is convertedinto an analog signal by a video digital/analog signal converter 123.The analog signals are adjusted to broadcasting signals in a NTSC/PALencoder 131 before being output for display.

The video decoding circuit 121 and the audio decoding circuit 127 areboth capable of outputting data transmitting request signals to thenavigator 117. The storage of data in the memory included in the videodecoding circuit 121 and the audio decoding circuit 127 may be adjustedbased on the size of those respective memories.

The video decoding circuit 121 may use its memory most efficiently byoutputting the data transmitting request signals to the navigator 117based on the storage volume of the video data recorded therein.

FIG. 6 is an internal block diagram showing the audio decoding circuit127 of the present invention which is also able to output the datatransmitting request signals according to the present invention.

According to FIG. 5, the audio decoding circuit 127 preferably outputsthe data transmitting request signal to the navigator 117.

The audio decoding circuit 127 of the reproduction apparatus of thepresent invention comprises a parser 139, an audio decoding unit 141 anda memory 143. The parser 139 receives a bit stream from the VBR buffer109 via a first input terminal and the data dividing control signalsfrom the navigator 117 via a second input terminal. The bit stream maybe received from VBR buffer 109 directly, or after being passed throughone or more of video decoding circuit 121 and graphics circuit 125, asshown in FIG. 5. Parser 139 extracts audio data from the bit streambased on the data dividing control signal from navigator 117, andoutputs that extracted audio signal to the audio decoding unit 141. Theparser 139 of audio decoding circuit 120 passes other, non-extractedsignals.

The audio decoding unit 141 within audio decoding circuit 120 generatesaudio data which corresponds to the original audio signals by decodingthe audio signals extracted by the parser 139. The audio decoding unit141 also executes data read/write operations. For example, the audiodecoding unit 141 may temporarily write the audio data in the memory143, or it may read and output the audio data recorded in the memory143. The audio decoding unit 141 may also monitor the storage volume ofthe audio data stored in the memory 143 and output the data transmittingrequest signals to the navigator 117 accordingly.

FIG. 7 is a detailed block diagram showing the audio decoding unit 141illustrated in FIG. 6. The audio decoding unit 141 may comprise a bitstream analyzing unit 151 for receiving and analyzing the bit streamoutput from the parser 139; and a data storage volume detecting unit(DSVDU) 153 for detecting the storage volume of the audio data stored inthe memory 143 which includes audio data analyzed in the bit streamanalyzing unit 151.

The audio decoding unit 141 may also comprise a control unit 155 foracknowledging the storage volume of the audio data stored in the memory143 upon receiving signals output from the data storage volume detectingunit 153, and for outputting an audio data transmitting request signalor an audio data transmitting stopping signal to the navigator 117 basedon the acknowledged storage volume. The control unit 155 also determineswhether the audio data being analyzed in the bit stream analyzing unit151 is invalid data or normal data. This determination can be made by,e.g., counting the number of bytes included in the received audio dataand comparing that number to a number of bytes in a normal audio dataunit. The control unit 155 controls the read/write operation of theaudio data output from the bit stream analyzing unit 151 in accordancewith the storage volume of the audio data of the memory 143. The controlunit 155 also controls the operations of other circuit subunits (notshown in the attached drawings) included in the audio decoding unit 141.

Under the control of the control unit 155, the audio data of one normalframe being output from the memory 143 is decoded by a multiplexer 157and an Inverse Discrete cosine ConverTing unit (IDCT) 159 according tothe time-frequency converting method, and then the decoded audio data isoutput. As seen in FIG. 5, the audio signal data output through the IDCT159 is converted by the audio digital/analog signal converter 129 intoaudio analog signals, which are output through a speaker or other audiooutput device (not shown in the attached drawings).

In other words, the audio decoding unit 141 adjusts the rate which theaudio signals are being input thereto. Audio decoding unit 141 istherefore able to decode the audio signals typically associated with onenormal frame by generating the data transmitting request signal or thedata transmitting stopping signal based on the bytes counting operationperformed by the control unit 155, and by acknowledging the storagevolume of the audio data stored in the memory 143 in accordance with thedetecting signal of the data storage volume detecting unit 153.

FIG. 8 is an internal block diagram showing the data storage volumedetecting unit 153 illustrated in FIG. 7. As shown in FIG. 8, the datastorage volume detecting unit 153 comprises: a last address detectingunit 161 for detecting the last address stored in the memory 143; areference address storage means 163 for storing a reference addresswhich will be compared with the last address stored in the memory 143 todetect an overflow/underflow; a comparing unit 165 for comparing anaddress detected by the last address detecting unit 161 with thereference address stored in the reference address storage means 163; andan overflow/underflow detecting unit 167 for detecting theoverflow/underflow of the memory 143 based on the comparison of thecomparing unit 165. The subunits of the data storage volume detectingunit 153 may be implemented as software as well as hardware.

The detecting operation of the storage volume of the data stored in thememory 143 by the data storage volume detecting unit 153 is nowdescribed with reference to FIG. 8. The comparing unit 165 compares thelast address detected by the last address detecting unit 161 with thereference address of the reference address storage unit 163, and outputsan comparing signal used to control whether the overflow/underflowdetecting unit 167 outputs an overflow/underflow state signal.

FIG. 9 is a detailed block diagram showing the control unit 155illustrated in FIG. 7. As shown in FIG. 9, the control unit 155comprises: a counter 181 for counting bytes of the audio data outputfrom the bit stream analyzing unit 151; a header data detecting unit 183for detecting the header data from the audio data output from the bitstream analyzing unit 151; and an invalid data detecting unit 185 fordetecting invalid data by based on the result of the counter 181 and theheader data detecting unit 183.

The control unit 155 further comprises a Central Processing Unit (CPU)187 for controlling a read/write operation into both a dummy datagenerating unit 189 and the memory 143 based on output signals of theinvalid data detecting unit 185. Also, the CPU 187 outputs the datatransmitting stopping signal or the data transmitting request signal tothe navigator 117 in response detection of an overflow/underflow byDSVDU 153.

When the audio signal detected in the invalid data detecting unit 185 isless than one normal frame (1536 bytes), the CPU 187 controls the dummydata generating unit 189 to generate dummy data which is stored in thememory 143 to make a complete normal frame. That is, by mixing the dummydata, the length of the input audio signal is adjusted into one normalframe.

On the other hand, when the audio signals detected in the invalid datadetecting unit 185 is longer than one normal frame, the CPU 187 turnsoff data writing into the memory 143, effectively preventing any audiosignals beyond one normal frame (1536 bytes) to be written from the bitstream analyzing unit 151 into the memory 143. Selectively, if the audiosignals beyond one normal frame (1536 bytes) are already written, theCPU 187 may control the memory 143 so that the audio signals areoverwritten by the audio signals of the next frame.

FIG. 10 is a state diagram showing the memory 143 of the audio decodingcircuit 127 illustrated in FIG. 6. The reference address storage unit163 (shown in FIG. 8) stores the reference addresses corresponding tothe underflow point and overflow point, which addresses depend on thesize of the memory 143. The overflow/underflow detecting unit 167outputs an overflow state signal when the address of the last datastored in the memory 143 is over the reference address corresponding tothe overflow point, and an underflow state signal when the last addressof the data stored in the memory 143 is under the reference addresscorresponding to the underflow point.

According to the overflow/underflow state signal detected from theoverflow/underflow detecting unit 167, as shown in FIG. 8, the controlunit 155 outputs the data transmitting stopping signal/data transmittingrequest signal. Undesired errors, which are otherwise generated by thememory 143 of the audio decoding circuit 127, are therefore prevented.Consequently, the memory 143 can be used most efficiently.

In the following, the method for compensating the reproduced audiosignals of the optical disc according to the present invention will bedescribed in detail.

As shown in FIG. 2, the DVD 1 records user data composed of thevideo/audio data, and system data used during the reproduction of theuser data. With reference to FIG. 5, these data are read and reproducedas signals by the optical pick-up apparatus 103. The reproduced signalsare output after being amplified in the high frequency amplifyingcircuit 10. The signals output from the high frequency amplifyingcircuit 105 are corrected by ECC 107, and output to VBR buffer 109 wherethey are temporarily stored.

The VBR buffer 109 generates a bit stream based on the signalstemporarily stored therein. The bit stream is input from VBR buffer 109into the navigator 117 and data decoding circuit unit 120. Navigator 117decodes the signals of the system data and then executes the datadividing controlling operation. That is, the navigator 117 controls thedata decoding circuit unit 120 so that the bit stream is decoded by thevideo decoding circuit 121 if the input bit stream represents the videodata, and the bit stream is decoded by he audio decoding circuit 127 ifthe bit stream represents audio data. Similarly, the bit stream isdecoded by the graphics circuit 125 if the bit stream represents captiondata.

With reference to the audio decoding circuit 127 in FIG. 6, the audiodecoding unit 141 in FIG. 7 and the control unit 155 in FIG. 9, theextracting operation of the audio decoding circuit 127 and itssignal-processing operation will be explained.

First, the navigator 117 determines the types of signals represented bythe bit stream input from VBR buffer 109. When the signals in the bitstream represent the audio data, the navigator 117 controls the audiodecoding circuit 127 to input the bit stream received by the parser 139of the audio decoding circuit 127 into the audio decoding unit 141. Theaudio data being input into the audio decoding unit 141 is analyzed inthe bit stream analyzing unit 151, and then stored in the memory 143.

In the above process of reproducing the optical disc, the data stored onthe optical disc is processed in units of frames. When the audio data isbeing stored in the memory 143, the control unit 155 determines whetherthe reproduced signals of the audio data signals having the length ofone normal frame. If the length of the reproduced signals of the audiodata is not of normal length (i.e., is not 1536 bytes), the control unit155 executes the operation for compensating the length of the reproducedaudio signals to adjust the reproduced signals to signals is of onenormal frame.

FIG. 11 is a flow chart illustrating the method for compensating thereproduced audio signals in the audio decoding circuit 127 according tothe present invention. FIG. 12 is a flow chart showing the method ofprocessing of the invalid data illustrated in FIG. 11. FIG. 13 is a flowchart showing the method of processing an overflow condition illustratedin FIG. 11. FIG. 14 is a flow chart showing the method of processingaccording to an underflow illustrated in FIG. 11.

As shown in FIG. 11, the initial value of the bytes counter 181 is setto ‘0’ (zero) (step 1101), and the header data detecting unit 183detects header data from audio data output by bit stream analyzing unit151 (step 1103).

As illustrated in FIG. 2, one frame of audio data typically includes1536 bytes of data, including header data, user data and an errorcorrecting codes (e.g., Cyclic Redundancy Code CRC). The header data isplaced before the user data which may be either one of the video/audiosignals, and the user audio data is placed after the header data. Thus,the detection of the header data may be used to determine beginning ofthe one frame of audio data.

When the header data is detected in step 1103, the bytes counter 181counts the bytes of the data being output by the bit stream analyzingunit 151 (step 1105), and the memory 143 stores the audio data output bythe bit stream analyzing unit 151 (step 1107).

The steps of counting the bytes of the audio data received from VBRbuffer 109 and of concurrently storing that audio data in the memory 143(steps 1105 and 1107) are repeatedly executed until the header data ofnext frame is detected by the header data detecting unit 183 (step1109).

Referring again to FIG. 9, the bytes counter 181 and header datadetecting unit 183 send data to CPU 187 via invalid data detecting unit185. In addition, bytes counter 181 transmits a counting result, andheader data detecting unit 183 transmits a detecting signal. The invaliddata detecting unit 185 detects whether the audio data input is invaliddata or normal data by counting the bytes of the data input until theheader data of the next frame is detected (step 1111), normal datahaving a length equal to one normal frame (1536 bytes).

If the number of bytes in a frame of audio data is determined by counter181 to exceed 1536 bytes in said step 1111, the audio data is determinedto be invalid data. When the audio data is determined to be invalid, itis processed by the CPU 187 (step 1113). In other words, the processingof the invalid data in the step 1113 will be executed when the length ofthe one frame of the audio data input is not 1536 bytes.

FIG. 12 shows the processing of the invalid data illustrated in FIG. 11.While processing invalid data, it is first determined whether theinvalid frame of audio data received from VBR buffer 109 is larger orsmaller than 1536 bytes (step 1201). If it is determined that theinvalid frame of audio data is smaller than 1536 bytes in step 1201, theCPU (refer to FIG. 9) turns off the error correcting code(CRC) in ordernot to execute the correction of errors included in the audio data (step1203). Meanwhile, the CPU 187 controls the dummy data generating unit189 to generate the dummy data, and then stores the generated dummy datainto the memory 143 (step 1205). The dummy data will be repeatedlygenerated and stored until the audio data reaches 1536 bytes.

On the other hand, if it is determined that the invalid frame of audiodata is larger than 1536 bytes by step 1201, the CPU (refer to FIG. 9)turns off the error correcting code(CRC) in order not to execute thecorrection of errors included in the audio data (step 1207). Meanwhile,the CPU counts the audio data input, and removes the data following the1536 th byte (step 1211). The remaining data may be removed bydiscontinuing writing function to the memory 143 in the step of storingthe audio data into the memory 143, effectively halting storage of theremaining data in the memory 143. Alternatively, the remaining data maybe removed by overwriting the remaining data with the audio data of thenext frame, if the remaining data has already been stored in the memory.

Once the audio data is adjusted so that the length of one frame of theaudio data is 1536 bytes in step 1205 or step 1211, the processing ofthe invalid data is terminated, and the reproduction process returns tostep 1115 in FIG. 11. If the above-described processing of the invaliddata is executed, the length of one resulting frame audio data willbecome one normal frame length (1536 bytes).

At step 1115, the CPU 187 continuously monitors, during the course ofstoring the audio data in the memory 143, whether an interrupt signalindicating overflow of the memory 143 is input from the data storagevolume detecting unit 153. Additionally, the CPU 187 continuouslymonitors whether an interrupt signal indicating underflow of the memory143 is input from the data storage volume detecting unit 153 (step1119).

The overflow and underflow of the memory 143 is detected (in step 1115)by the data storage volume detecting unit 153, as shown in FIGS. 7 and8, based on the storage volume of the data stored in the memory 143 asfollows. First, the last address detecting unit 161 detects the addressof the last data having been stored in the memory 143, and outputs thedetected last address to the comparing unit 165. The comparing unit 165compares the last address with the reference addresses for overflow andunderflow, respectively. The overflow/underflow detecting unit 167outputs the interruption signal of either overflow or underflow based onthe current storage volume of the data stored in the memory 143. Theinterruption signal is input into the CPU 187, and according to therespective interruption signal the CPU 187 outputs the data transmittingstopping signal or the data transmitting request signal to the navigator117.

Thus, detection of memory 143 overflow in said step 1115 means thatexcessive data is stored in the memory 143 and that the address detectedby the last address detecting unit 161 is over the reference address,i.e., the memory 143 has overflowed. Therefore, the CPU 187 outputs thedata transmitting stopping signal to the navigator 117.

So long as an interruption signal indicating an overflow of the memory143 is being output from the data storage volume detecting unit 153, theCPU 187 executes an overflow processing routine as indicated by step1117. The overflow processing routine of step 1117 is executed when thestorage volume of the data stored in the memory 143 of the audiodecoding circuit 127 is over a predetermined value.

FIG. 13 shows, in more detail, the overflow processing routineillustrated in FIG. 11. In that routine, the CPU 187 outputs the datatransmitting stopping signal to the navigator 1117 (step 1301). The CPU187 then determines whether the bit stream analyzing unit 151 transmitsany audio data (step 1303). If audio data is transmitted, the CPU 187turns off the writing of the memory 143, thereby inhibiting the writingof the memory with the transmitted audio data (step 1305). If audio datais not transmitted, the CPU 187 examines whether the overflow of thememory 143 continues (step 1307). If the overflow flag of the memory 143remains active, the reproduction process returns to the step 1301, andsteps 1301 to 1307 are repeated.

While the above-described process is executed, the data storage volumedetecting unit 153 detects the storage volume of the data stored in thememory 143 and outputs state signals to the CPU 187. If it is concludedthat the overflow of the memory 143 is released by the state signal, theCPU 187 outputs the data transmitting request signal to the navigator117. Simultaneously, the writing operation is resumed to store the audiodata being output from the bit stream analyzing unit 151 into the memory143 (step 1309). Thus, the processing of the overflow ends and thereproduction process returns to step 1119 in FIG. 11.

The fact that the memory 143 is underflowed in step 1119 means that theaddress detected by the last address detecting unit 161 is less than thereference address for underflow, and there exists an excess amount ofvacant storage space in the memory 143. Therefore, theoverflow/underflow detecting unit 167 outputs the interruption signal ofunderflow to the CPU 187, and the CPU 187 outputs the data transmittingrequest signal to the navigator 117. More specifically, if the memory143 is in underflow, the CPU 187 executes the data processing operationaccording to the processing of the underflow processing routine (step1121).

FIG. 14 shows in more detail the processing of the an underflowsituation illustrated in FIG. 11. The CPU 187, in the initial stage ofthe processing of the underflow, stores the audio data being output fromthe bit stream analyzing unit 151 into the buffer in the unit 151, andupdates the buffer (step 1401). The CPU 187 then outputs the datatransmitting request signal to the navigator 117 (step 1403). The CPU187 determines whether there is any audio data transmitted by said step1403 (step 1405). If audio data is transmitted, the CPU 187 continues tostore the audio data into the memory 143. If no audio data istransmitted, the CPU 187 outputs the data stored in the buffer, whichdata is stored into the memory 143 (step 1407). That is, a portion ofaudio data previously received is redundantly stored in memory 143during an underflow condition if no new data is transmitted.Alternatively, dummy data, a default data pattern, or an average of somegroup of previously transmitted or stored audio data may be stored inmemory 143 under such conditions.

During the execution of the above-described process, the CPU 187examines whether the underflow condition of the memory 143 remains ornot (step 1409). If the underflow condition remains, the reproductionprocess returns to the step 1401, and said steps 1401 to 1409 arerepeated. While the underflow condition remains without any transmitteddata, the data stored in the buffer is repeatedly output and stored inthe memory 143.

Once the underflow of the memory 143 is released by the state signaloutput from the data storage volume detecting unit 153, the CPU 187clears the buffer (step 1411), and the processing of the underflow endsso that the reproduction process returns to step 1123 in FIG. 11.

The multiplexer 157 and the IDCT 159 are used to decode audio signalsbeing output from the memory 143 into decoded audio data correspondingto the original signals based on a time-frequency converting method(refer to FIG. 7) (step 1123). The decoded audio data is then output tothe audio digital/analog converter 129 (refer to FIG. 5). The decodedaudio signal data being output from the audio decoding circuit 127 isthen converted into analog signals by the audio digital/analog converter129, before being output to the speaker, etc. (not shown in the attacheddrawings).

FIG. 15 shows the audio decoding unit 141 of a second preferredembodiment of the present invention. As shown in FIG. 15, the bit streamanalyzing unit 251 analyzes data in the bit stream input from the parser139, the analyzed data being temporarily stored in the memory 143. Thebit stream output from the bit stream analyzing unit 251 is input intothe control unit 255, where the length of the audio data input iscompared with the length of one normal frame. The data storage volumedetecting unit 253 detects the data storage volume of the audio dataoutput from the memory 143, and outputs a state signal according to thedata storage volume detected.

In accordance with the state signal, the control unit 255 generates theaudio data transmitting request signal or the audio data transmittingstopping signal. The audio data output from the memory 143 is decoded bythe multiplexer 257 and IDCT 259, and the decoded data is output.

The audio decoding unit 141 according to the second preferred embodimentgenerates a data transmitting request signal if a minimum predeterminedamount of vacant storage space exists in the memory 143, and generates adata transmitting stopping signal if maximum predetermined amount ofvacant storage space does not exist in the memory 143. That is,according to the second preferred embodiment, a data transmittingstopping signal can be sent to the navigator 117 to inhibit the supplyof data into the audio decoding circuit 127 when an overflow conditionexists in the memory 143, and a data transmitting request signal can besent to the navigator 117 to request data when an underflow conditionexists in the memory 143. However, the controlling operation of theaudio decoding unit 141 of the first preferred embodiment (FIG. 7), bywhich the dummy data is directly and repeatedly stored in, or outputfrom, the memory 143, is impossible according to this preferredembodiment.

FIG. 16 shows the control unit 155 of a third preferred embodiment ofthe present invention. As shown in FIG. 16, the control unit 155according to this preferred embodiment comprises: a counter 191 forcounting the bytes of the audio data being output from the bit streamanalyzing unit 151; a header data detecting unit 193 for detecting theheader data from the audio data being output from the bit streamanalyzing unit 151; and an invalid data detecting unit 195 for detectinginvalid data upon receiving detecting signal output from the header datadetecting unit 193.

Also, the control unit 155 of this preferred embodiment comprises aCentral Processing Unit (CPU) 197 for controlling the read or writeoperation into the memory 143 based on signals output from the invaliddata detecting unit 195, and for outputting a data transmitting stoppingsignal or a data transmitting request signal to the navigator 117according to the overflow/underflow state signal detected in the datastorage volume detecting unit 153.

No separate dummy data generating unit 189 exist in the control unit 155of this preferred embodiment. Therefore the CPU 197 adjusts invalid datato the normal data having one normal frame length by storing the datainput into the memory 143 previously repeatedly or by inserting thedummy data into the invalid data (refer to FIG. 17C). In this regard,the dummy data may be inserted by well-known methods, for example, byinserting a desirable portion of a sample wave into the invalid data. Itshould be obvious to those skilled in the art that the tone quality ofthe signals according to the above method can be made to besubstantially similar from original signals. When the length of theaudio data input is longer than the length of the data of the one normalframe, as in FIG. 9, the storage of the data exceeding a normal framewill be inhibited.

FIGS. 17A-17F are diagrams showing the output waveforms of invalid dataand the compensated audio signals when the invalid data are input.

As shown in FIG. 17A, when an invalid data whose length is less than thenormal length (e.g., 1216 bytes) is input, signals of abnormal waveformswill be output absent compensation, as shown in FIG. 17B. That is, noiseoccurs at the portion of the signal representing invalid data.

According to the present invention, invalid data whose length is greaterthan the normal length may be monitored and neutralized by eitherinhibiting storage of that data into the memory 143 during the writingoperation or by removing that data during the reading operation, asshown in FIG. 17C.

When invalid data has a length of less than the normal length, theportion of the signal representing invalid data may be replaced withdummy data, muted data, or data representing previously stored data. Ifinvalid data is replaced with muted data, as shown in FIG. 17D, thememory's writing operation will be turned off while the invalid data isinput into the memory 143, so that the invalid data will be replaced bymuted data, e.g., in a signal mute unit (not shown in the attacheddrawings). For instance, such a single mute unit can be used in place ofdummy data generating unit 189 in FIG. 9. That is, instead of storingdummy data using dummy data generating unit 189, a signal muting unitmay be used to store muted data. The muted data may be added to theinvalid audio data before storage of that audio data, the muted data maybe stored in place of the invalid audio data.

FIG. 17E shows waveform of reproduced audio signals compensated inaccordance with that above-described preferred embodiment of the presentinvention, in which the output of the audio data is adjusted when anunderflow condition is detected by repeatedly outputting the data storedin the memory 143. Also, FIG. 17F shows output waveform of the data towhich a dummy data is added as described previously. For instance, whenthe invalid data is input having a length of 1216 bytes, which issmaller than one normal frame (1536 bytes), this preferred embodiment ofthe present invention adjusts the invalid data to normal length byadding dummy data to the invalid data.

While there have been illustrated and described what are at presentconsidered to be preferred embodiments of the present invention, it willbe understood by those skilled in the art that various changes andmodifications may be made, and equivalents may be substituted forelements thereof without departing from the true scope of the presentinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teaching of the presentinvention without departing from the central scope thereof. Therefor, itis intended that the present invention not be limited to the particularembodiment disclosed as the best mode contemplated for carrying out thepresent invention, but that the present invention includes allembodiments falling within the scope of the appended claims.

The foregoing description and the drawings are regarded as including avariety of individually inventive concepts, some of which may liepartially or wholly outside the scope of some or all of the followingclaims. The fact that the applicant has chosen at the time of filing ofthe present application to restrict the claimed scope of protection inaccordance with the following claims is not to be taken as a disclaimeror alternative inventive concepts that are included in the contents ofthe application and could be defined by claims differing in scope fromthe following claims, which different claims may be adopted subsequentlyduring prosecution, for example, for the purposes of a continuation ordivisional application.

1. A method for controlling an audio memory of an audio decoding circuitincluded in a data decoding unit having a video decoding circuit, saidmethod comprising: detecting an amount of data stored in said audiomemory, and an address of a last audio data stored in said audio memory;comparing the detected address of the last audio data stored in saidaudio memory with a reference address, which corresponds to apredetermined lower threshold for said amount of data stored in saidaudio memory, and determining whether said amount of data stored in saidaudio memory is less than said predetermined lower threshold based onthe comparison of the detected address with the reference address; andrequesting additional audio data to be stored into said audio memoryindependently of processing in the video decoding circuit when saidamount of data stored in said audio memory is less than saidpredetermined lower threshold.
 2. The method recited by claim 1, furthercomprising: storing data that is representative of previously storedaudio data when additional audio data is not available for storage intosaid audio memory while said amount of data stored in said audio memoryis less than said predetermined lower threshold.
 3. The method recitedby claim 1, further comprising: storing dummy data into said audiomemory while said amount of data stored in said audio memory is lessthan said predetermined lower threshold.
 4. An apparatus for controllingan audio memory of an audio decoding circuit included in a data decodingunit having a video decoding circuit, said apparatus comprising: avolume detecting unit for detecting an amount of data stored in saidaudio memory, said volume detecting unit comprising a last addressdetecting unit for detecting an address of a last audio data stored insaid audio memory; a comparing unit for comparing the detected addressof the last audio data stored in said audio memory with a referenceaddress, which corresponds to a predetermined lower threshold for saidamount of data stored in said audio memory, and determining whether saidamount of data stored in said audio memory is less than saidpredetermined lower threshold based on the comparison of the detectedaddress with the reference address; and a controller including a signalgenerator, said signal generator generating a data transmission requestsignal requesting additional audio data to stored into said audio memoryindependently of processing in the video decoding circuit when saidamount of data stored in said audio memory is less than saidpredetermined lower threshold.
 5. The apparatus recited by claim 4,wherein said controller stores data that is representative of previouslystored audio data when additional audio data is not available forstorage into said audio memory while said amount of data stored in saidaudio memory is less than said predetermined lower threshold.
 6. Theapparatus recited by claim 4, wherein said controller further includes adummy data generator for generating dummy data to be stored in saidaudio memory while said amount of data stored in said audio memory isless than said predetermined lower threshold.
 7. A method forcontrolling an audio memory of an audio decoding included in a datadecoding unit having a video decoding circuit, said method comprising:detecting an amount of data stored in said audio memory by detecting anaddress of a last audio data stored in said audio memory; comparing thedetected address of the last audio data stored in said audio memory witha reference address, which corresponds to a predetermined upperthreshold for said amount of data stored in said audio memory, anddetermining whether said amount of data stored in said memory is greaterthan aid predetermined upper threshold based on the comparison of thedetected address with the reference address; and generating a datatransmission stopping signal independently of processing in the videodecoding circuit when said amount of data stored in said audio memory isgreater than said predetermined upper threshold until said amount ofdata stored in said audio memory is less than or equal to saidpredetermined upper threshold.
 8. The method recited by claim 7, furthercomprising: halting storage of additional audio data in said memory whensaid amount of data stored on said memory is greater than saidpredetermined upper threshold.
 9. An apparatus for controlling an audiomemory of an audio decoding circuit included in a data decoding unithaving a video decoding circuit, said apparatus comprising: a volumedetecting unit for detecting an amount of data stored in said audiomemory, wherein said volume detecting unit comprising a last addressdetecting unit for detecting an address of a last audio data stored insaid audio memory; a comparing unit for comparing the detected addressof the last audio data stored in said audio memory with a referenceaddress, which corresponds to a predetermined upper threshold for saidamount of data stored in said audio memory, and determining whether saidamount of data stored in said audio memory is greater than saidpredetermined upper threshold based on the comparison of the detectedaddress with the reference address; and a controller including a signalgenerator, said generator generating a data transmission stopping signalindependently of processing in the video decoding circuit when saidamount of data stored in said audio memory is greater than saidpredetermined upper threshold until said amount of data stored in saidaudio memory is less than or equal to said predetermined upperthreshold.
 10. The apparatus recited by claim 9, wherein said controllerhalts storage of additional audio data in said memory when said amountof data stored on said memory is greater than said predetermined upperthreshold.
 11. A method for decoding a compensated audio data bycontrolling an audio memory of an audio decoding circuit included in adata decoding unit having a video decoding circuit, said methodcomprising: decoding, by the audio decoding circuit, the compensatedaudio data, wherein compensating the audio data comprises: detectinginvalid data based on count information associated with the audio data;and generating dummy data based on the detecting of the invalid data,the dummy data being repeatedly generated until audio data reaches apredefined length of bytes, said decoding comprising: detecting anamount of data stored in said audio memory, the detecting comprising:detecting an address of a last audio data stored in said audio memory,comparing the detected address of the last audio data stored in saidaudio memory with a reference address corresponding to either apredetermined lower threshold or a predetermined upper threshold forsaid amount of data stored in said audio memory, determining whethersaid amount of data stored in said audio memory is less than saidpredetermined lower threshold based on the comparison of the detectedaddress with the reference address, and determining whether said amountof data stored in said audio memory is greater than said predeterminedupper threshold based on the comparison of the detected address with thereference address; requesting additional audio data to be stored intosaid audio memory independently of processing in the video decodingcircuit when said amount of data stored in said audio memory is lessthan said predetermined lower threshold; and generating a datatransmission stopping signal independently of processing in the videodecoding circuit when said amount of data stored in said audio memory isgreater than said predetermined upper threshold.
 12. The method of claim11, wherein the count information indicates a length of the audio data.13. The method of claim 11, wherein the decoding includes an inversediscrete cosine converting transformation.